* Corresponding author. Tel.: #49-931-888-5813; fax: #49- 931-888-5143. E-mail address: bacher@physik.uni-wuerzburg.de (G. Bacher). Journal of Crystal Growth 214/215 (2000) 150 } 153 Semimagnetic (Cd,Mn)Te single quantum dots * technological access and optical spectroscopy T. Ku K mmell, G. Bacher*, M.K. Welsch, D. Eisert, A. Forchel, B. Ko K nig, Ch. Becker, W. Ossau, G. Landwehr Technische Physik, Universita ( t Wu ( rzburg, Am Hubland, D-97074 Wu ( rzburg, Germany Experimentelle Physik III, Universita ( t Wu ( rzburg, Am Hubland, D-97074 Wu ( rzburg, Germany Abstract An alternative technological approach for the realization of (Cd,Mn)Te nanostructures is presented. Focused ion beam lithography and subsequent thermal annealing are used for a lateral modulation of the bandgap, allowing both, the realization of quantum wires and quantum dots with adjustable size and a well-de"ned lateral potential. Due to the high quantum e$ciency of the buried nanostructures, photoluminescence spectroscopy even on single quantum dots becomes accessible, allowing an experimental insight on optical transitions in three-dimensionally con"ned semimagnetic structures.  2000 Elsevier Science B.V. All rights reserved. PACS: 78.66.Hf; 73.20.Dx; 71.35.Lk Keywords: CdMnTe; Single quantum dots; Focused ion beam lithography 1. Introduction Due to size and composition #uctuations, optical transitions in semiconductor quantum dot en- sembles are usually characterized by in- homogeneous broadening e!ects. This can be suppressed completely by studying single quantum dots and recently, a variety of experimental tech- niques, including mesa etching, nanostructured masks, -photoluminescence (PL) measurements or near-"eld scanning optical microscopy, have been developed [1}4]. Most of the experiments have been performed on non-magnetic III}V or II}VI compounds, and new experimental insight, e.g. on the homogeneous linewidth of single exciton transitions, the "ne structure of optical transitions, multiexciton formation or spin relaxation was ob- tained [2,5}9]. It is well known, that CdTe- or ZnSe-based II}VI compounds o!er the possibility to include transition metals like, e.g. Mn in the crystal matrix [10], and a variety of experimental studies on semimagnetic bulk or quantum wells have been performed, investigating, e.g. the inter- action between the exciton spin and the spins of the Mn atoms in the surrounding matrix. On the other hand, investigations on Mn-containing quantum dots are quite scarce up to now and to our knowledge limited to quantum dot ensembles [11,12]. 0022-0248/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 0 0 ) 0 0 0 5 2 - X